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<p>It sounds like the linker has to be aware of the .eh_frame
section details to be able to generate .eh_frame_hdr and eliminate
duplicate CIEs, right?</p>
<p> So, is there any difference whether it knows that in one place
or two?<br>
</p>
Best Regards,<br>
Igor Kudrin<br>
C++ Developer, Access Softek, Inc.<br>
<br>
<div class="moz-cite-prefix">On 27-Oct-17 3:43, Rui Ueyama via
llvm-dev wrote:<br>
</div>
<blockquote
cite="mid:CAJENXgvaeZxyDUw2raEg19e=Kmzf7e1c5MR9S+8AdPceoUR5=g@mail.gmail.com"
type="cite">
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<div class="gmail_extra">
<div class="gmail_quote">On Thu, Oct 26, 2017 at 1:13 PM,
Evgeny Astigeevich <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:Evgeny.Astigeevich@arm.com" target="_blank">Evgeny.Astigeevich@arm.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
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lang="EN-GB">
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif">Hi,</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif">There
will be problems with eh_frame_hdr. Eh_frame_hdr
is needed to use the binary search instead of the
linear search. Having eh_frame per a function will
cause no eh_frame_hdr or multiple eh_frame_hdr and
will degrade search from binary to linear.</span></p>
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</blockquote>
<div><br>
</div>
<div>Linkers would combine .eh_frame sections into one
.eh_frame, so that's not an issue, no?</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
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lang="EN-GB">
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif"></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif">As
we create eh_frame_hdr in most cases there is no
problem to filter out garbage eh_frame sections.
If there is information about unused symbols, the
implementation is very simple. BTW there is no
need to do full decoding of eh_frame records to
remove garbage.</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif">Paul
is right there will be code size overhead.
Eh_frame is usually created per a compilation
module with common information in CFI. Multiple
eh_frames will cause a lot of redundant CFI. There
might be a case when the total size of redundant
CFIs will be greater than the total size of
removed garbage.</span></p>
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</blockquote>
<div><br>
</div>
<div>As I wrote in the previous message, I don't think
there's a size issue in link results because even existing
linkers merge CIEs by contents.</div>
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